This invention relates to an elevator rescue apparatus during the stoppage of power supply according to which a power-failure rescure circuit can be installed even when a current type inverter is employed.
In recent years, with the progress of control technology, the VVVF (variable-voltage and variable-frequency) control system has come into adoption also for elevator control apparatuses. The basic forms of this VVVF control system includes two types; the voltage type and the current type.
Of them, the former voltage type is arranged as shown in FIG. 2. This figure illustrates an example in which a power-failure rescue ciruit is applied to a conventional voltage type VVVF control system. Letters R, S and T in FIG. 2 indicate the respective phases of a three-phase A.C. power source not shown.
The phases R, S and T are connected to the corresponding input ends of converters 2 and 3 through the contacts 1 of a contactor. Each of the converters 2 and 3 constructs a three-phase bridge circuit out of thyristors SCR, and these converters 2 and 3 are connected in parallel.
A smoothing capacitor 4 is connected across the output ends of the converters 2 and 3, and a D.C. voltage obtained by rectifying three-phase A.C. power by means of the converter 2 is smoothed by the smoothing capacitor 4. The converter 3 is operated during the regeneration of an induction motor 6.
The output voltage of the converter 2 is applied to an inverter 5. The inverter 5 is constructed of transistors TR and diodes D. The diode D is connected across the emitter and collector of the corresponding transistor TR, and is formed unitarily with this transistor.
The inverter 5 inverts the output voltage of the converter 2 into a three-phase A.C. voltage of predetermined frequency and predetermined voltage value, with which the induction motor 6 is driven. The cage (not shown) of an elevator is driven by the induction motor 6.
In addition, the input ends of the converter 2 are connected to the input end of a charging circuit 8 through a transformer 7. The output of the charging circuit 8 is used for charging a battery 9. The anode of the battery 9 is connected to the positive side output end of the converters 2 and 3 through the contact 10 of a contactor, while the cathode of the battery 9 is connected to the negative side output end of the converters 2 and 3. The battery 9 is the power source of the rescue circuit in the case of the failure of the power supply.
Next, the operation of the prior-art system will be described. While the power supply is normal, the contacts 1 of the contactor are closed and the contact 10 of the contactor is open. Owing to the closure of the contacts 1 of the contactor, the voltages of the respective phases R, S and T of the three-phase A.C. power source are applied to the converter 2 and are converted into the D.C. voltage.
This D.C. voltage is smoothed by the smoothing capacitor 4, and is applied to the inverter 5. In the inverter 5, the smoothed D.C. voltage is inverted into the A.C. power of desired frequency and desired voltage by the use of the pulse width modulation technique, and the resulting A.C. power is fed to the induction motor 6. Thus, the induction motor 6 is driven to run the cage of the elevator. Since the technique of such a VVVF control is well known, it shall not be detailed here.
Assuming now that the converter 2 be used for the power operation in the up direction of the cage, the converter 3 is used for the regenerative operation. In this manner, the polarity of the voltage across both the terminals of the smoothing capacitor 4 remains unchanged, so that the direction of the current is inverted in accordance with the power or regenerative operation.
Meanwhile, when the power supply has stopped, the contacts 1 of the contactor are opened, and the contact 10 of the contactor is closed instead. At this time the electric power of the battery 9 is connected to the D.C. circuit through the contact 10 of the contactor, and it is inverted into A.C. power of variable voltage and variable frequency by the inverter 5. The subsequent operation is the same as in the case of the normal power supply.
The polarity of the voltage of the D.C. circuit shown in FIG. 2 is fixed, and the current direction thereof is inverted with the four-quadrant running of the power and regenerative operations.
In contrast, according to the current type, the current direction of a D.C. circiuit is fixed, and the voltage polarity thereof is inverted with the four-quadrant running. FIG. 3 shows an example of a system of the current type, in which the same portions as in FIG. 2 are assigned identical symbols.
The voltages of the respective phases R, S and T of a three-phase A.C. power source are applied to the input ends of a converter 2 through the contacts 1 of a contactor. The converter 2 constructs a three-phase bridge circuit in such a way that a diode D1 is connected in series with each of parallel circuits consisting of transistors TR and diodes D.
The output of the converter 2 is fed to an inverter 5 through a reactor 11. The inverter 5 is constructed of transistors TR and diodes D and D1 similarly to the converter 2. The inverter 5 inverts the D.C. output of the converter 2 into A.C. power of variable frequency and variable voltage, with which an induction motor 6 is driven.
This system of FIG. 3 differs from the system of FIG. 2 in that, since the diodes D1 are respectively connected to the transistors TR of the converter 2 and the inverter 5, the current direction remains unchanged, whereas the voltage polarity of the D.C. circuit is inverted in accordance with the power or regenerative operation.
As compared with the voltage type inverter shown in FIG. 2, this current type inverter shown in FIG. 3 does not include an element of short lifetime such as the capacitor (an electrolytic capacitor has a short lifetime).
Regarding the number of constituent elements, the voltage type inverter requires the thyristors and transistors totaling 18, whereas the current type inverter may include 12 such elements (the diodes are not taken into consideration because they are inexpensive). Accordingly, the current type is meritorious in economy etc. and will be increasingly adopted in the future.
The current type inverter, however, has had the disadvantage that a battery cannot be connected to the D.C. circuit at the time of the failure of the power supply because the voltage polarity changes.